Updated: May 20, 2021
Most dental compressors use desiccant dryers to remove moisture from the air. They use silicate beads. The "tower" that contains them is designed to be regenerating, using the air from the compressor to constantly dry the beads as they absorb moisture so a good desiccant dryer should last for years with very little maintenance.
If you're concerned about the condition of your desiccant media, remove the dryer from your lines and shake it. If the beads are in good condition, they will be loose and rattle when you shake the dryer assembly. When contaminated with moisture, they have a tendency to clump, so you'll just get a solid "thunk" as the mass of beads moves from one end of the tower to the other. This is an indication that it's time to replace the media. However, under normal circumstances, you can also manually regenerate your media.
Dump out the saturated beads and take them home. Put them on a cookie sheet in a conventional oven at about 275°F for 30-45 minutes and they should be as good as new again.
Of course, you can certainly get re-charge kits (a jug of beads) for a reasonable price from many sources as well.
Dry air is important to your dental equipment so it's important to keep an ear on your dryer to make certain it's doing the job for which it is intended.